Paper enclosed low density pad with septum



June 5, 1962 w. A. JACK 3,037,578

PAPER ENCLOSED LOW DENSITY PAD WITH SEPTUM Filed Sept. 9, 1957 INVENTORWax/ 4 A Jhc/f United States Patent Ofice 3,037,578 PAPER ENCLOSED LOWDENSITY PAD WITH SEPTUM William A. Jack, Hampton, N.J., assignor toJohns-Manville Corporation, New York, N.Y., a corporation of New YorkFiled Sept. 9, 1957, Ser. No. 682,669 3 Claims. (Cl. 181-33) Thisinvention relates to acoustical constructions and, more particularly, toimproved sound-absorbing units for use in conventional sound-absorbingapparatus.

Sound-absorbing units of the type comprising pads of fibrous material,such as mineral wool, wood fiber, glass fiber and the like, usuallyenclosed in a sound-pervious wrapper, have been employed heretofore inacoustical treatments as a sound-absorbing medium. The pads are insertedin a plurality of perforated metal pans supported from a wall orceiling, with each pan containing an individual sound-absorbing pad.

Heretofore, these pads have necessarily been formed of relatively highdensity mats, even though they are more expensive, because such matshave a higher efliciency of acoustical absorption over a wider range ofsound fre quencies than the lower density mats, as the latter mats havea relatively low acoustical coefficient in the high frequency range ofsound.

A main purpose of the present invention is to provide a new and improvedsound-absorbing unit characterized by a novel, laminated padconstruction employing fibrous material of much lower density than ithas been possible to employ usefully heretofore in acousticalconstructions.

A further purpose of the present invention is to provide a new andimproved sound-absorbing unit of simple and light weight construction,which shows excellent acoustical efficiency over wide range offrequencies.

A sound-absorbing or acoustical unit constructed in accordance with thepresent invention consists of a pad comprising a plurality of layers oflight weight, fibrous material, a septum interposed between such layers,and a paper Wrapper enclosing the laminated construction; the layers andwrapper cooperate to give the unit a high acoustical eificiency in thelow frequency range of sound while the layers and septum cooperate togive the unit a high acoustical efiiciency over the high frequencyrange. The three elements consequently cooperate with each other to givethe unit a high coefficient of sound absorption over a wide band of lowand high frequencies These several features of the present invention aredescribed in detail below in connection with the accompanying drawing,in which like numerals designate like parts, and in which:

FIG. 1 is a perspective view of a sound-absorbing unit embodying thepresent invention; and

FIG. 2 is a broken vertical section, on an enlarged scale, takensubstantially along the line 2-2 in FIG. 1.

Referring now in detail to the drawing, the illustrated embodiment ofthe sound-absorbing unit of the present invention is indicated generallyby the reference numeral 10, and comprises a pad 12 of porous,light-weight, soundabsorbing material composed of a mat or felt offibrous or granular material, such as mineral Wool, wood fiber, glassand the like, having a suitable binder dispersed throughout the mat. Asin the conventional practice, the sheet or layer of felted fibers inaccordance with the instant invention is formed with an intermingled,and preferably heat setting, binder, such as a drying oil. The layer iscompressed to the desired density and the binder is set by applicationof heat, whereby a relatively resilient mat is produced. The mat used isrelatively light in weight, being of the order of 3 pounds per cubicfoot and less than about 6 pounds per cubic foot, as contrasted with3,037,578 Patented June 5, 1962 mats of 8-16 pounds per cubic footpresently in common use. The resultant mat is also relatively shapesustaining and, due to its relative rigidity, may be dimensioned withreasonably accurate limits.

In accordance with the present invention, the felted pad 12 is composedof two sheets or layers 16 and 18 of the interfelted fibers laminatedtogether. The mat of the pad 12 may be sliced at the center to form thetwo layers 16 and 18 if it is sufficiently thick or, if it is relativelythin, two separate, preformed sections may be employed as the separatelayers. A septum 20 of a layer or sheet of thin, flexible,air-impervious material, which is also sound-pervious and desirablyflameproofed, such as flameproofed krfat paper and the like, isinterposed between the layers 16 and 18 and may be adhered thereto inany convenient manner, as by cementing. As is well known, soundabsorption is obtained through sound decadence in the numerousinterstices and openings provided in the fibrous structure. With the useof light weight material, it has been discovered that the absorption ofthe high range of frequencies is sharply reduced. The septum 20cooperating with the layers 16, 18 compensates for this loss by giving adesirable increase in sound-absorption of such high frequencies.

The pad assembly 12, having any suitable thickness, say about 1 to 4inches, is enclosed by a paper wrapper 14, in any suitable manner. Thewrapper 14, of relatively thin, flexible and sound-pervious butair-impervious material similar to that used in septum 20, may be formedinto a bag of accurate dimensions, as by being cemented along the topoverlapping marginal portions, as indicated at 22, and at one endthereof. The bag is held with the other end open and distended, and thepad 12 is slightly compressed between its outer surfaces and insertedinto the open end of the bag 14. The bag may then be sealed by cementinga suitable closure flap 24 over the open end. Alternatively, the wrapper14 may be simply folded over the pad 12 and sealed at the overlappingportions thereof. The wrapper 14, in addition to maintaining the twolayers 16 and 18 and the septum 20 in proper relationship, serves alsoto prevent air breathing through portions of the pad 12, therebypreventing soiling of the acoustical facing and also prevents fallingout of fibers or granules from the pad 12. At the same time, the wrapperacts as an additional low frequency sound absorber, increasing therebythe sound-absorption of the pad over a wider range.

It will thus be appreciated that in the laminate or sandwichconstruction of the sound-absorbing unit 10 of the present invention, alow-density, inexpensive fibrous material is employed in lieu of thehigher density, more expensive materials. To compensate for the loss ofsoundabsorption in the high-frequency range, a paper septum is utilizedbetween layers of the inexpensive fiber. To increase the soundabsorption in the low frequency range and to provide a proper retainerfor the materials, the laminate structure is enwrapped in a papercovering or bag.

With such an enwrapped laminated structure, acoustical efiicienciesobtained are comparable to the efficiencies of pads utilizing a higherdensity mat. However, the relative cost of the units has been reducedsharply, principally in the reduction of the amount of material used inthe mat, as the relative cost of the septum and wrapper is minorcompared to the cost of the pad.

Having thus described my invention in rather full detail, it will beunderstood that these details need not be strictly adhered to but thatvarious changes and modifications may suggest themselves to one skilledin the art, all falling within the scope of the invention as defined bythe subjoined claims.

What I claim is:

1. An acoustical unit comprising a sound-absorbing, porous,self-sustaining pad, said pad comprising layers of relatively lightweight, fibrous material having a density Within the approximate rangeof 3 to 6 pounds per cubic foot, a thin, paper-like, imperforate,sound-pervious septum interposed between said layers, and a soundpervious wrapper enclosing said pad and septum.

2. An acoustical unit comprising a sound-absorbing, porous pad, said padcomposed of a pair of layers of light-weight, fibrous material having amaximum density of approximately 6 pounds per cubic foot, a paper-thinrelatively flexible layer of sound-pervious material interposed betweens'aid layers of fibrous material, said layer of sound pervious materialbeing imperforate and a relatively flexible air impervious, soundpervious wrapper enclosing said pad.

3. A sound-absorbing unit comprising a preformed, porous pad assembly,said pad assembly including a pair of layer of sound-absorbing fibrousmaterial, said material having a density of less than about 6 pounds percubic foot, a relatively thin, sound-pervious septum interposed betweensaid layers, a sound-pervi0us, air-impervious paper wrapper enclosingsaid pad assembly, said material providing good sound absorbingefficiency in the lower frequency range of sound waves and the septumcooperating with the fibrous material to provide good sound absorbingefiiciency in the higher frequency range of the sound waves.

References Cited in the file of this patent UNITED STATES PATENTS1,915,611 Miller June 27, 1933 1,955,443 Spafford Apr. 17, 19342,064,327 Upson Dec. 15, 1936 2,357,115 Jack et al Aug. 29, 19442,802,764 Slayter et al Aug. 13, 1957 FOREIGN PATENTS 183,937Switzerland July 16, 1936

